Name one other game where they changed the way data is handled, I'll wait.
Before this gen, all decompression was being done on the CPU. That's the reason why BC games aren't loading in 2-seconds on the PS5 as next-gen first-party games like Astrobot, Spider-Man, and Demon's Souls did, and instead takes 30 seconds to 60 seconds. Any improvements you see are solely because of the increase in CPU power. Their code is to use CPU for loading and storage, not the decompressor unit (because there wasn't any on the PS4/Xbox One).
Remedy changed the way data is handled for the Ultimate Edition -- which means it is no longer only relying on the CPU but also tapping into the decompressor units, if available.